The present invention relates to a method and apparatus for environmental monitoring for identifying substances, such as organic contaminants, present in the environmental atmosphere or measuring concentrations of the substances.
The environmental monitoring, which is made for the purpose of identifying substances present in the environmental atmosphere or measuring concentrations of the substances, is required in various sites.
One example of the environmental monitoring is conducted in clean rooms where semiconductor devices are fabricated.
In fabricating semiconductor devices, various processes are conducted on the surfaces of semiconductor wafers in accordance with the purposes of the processes. In a front end process, a cleaning treatment is made on the surfaces of wafers by a wet cleaning method using various chemicals or deionized water, a dry cleaning method using UV light or plasmas or others, or other methods, and then a surface modifying treatment, such as oxidation, etc., is made. The clean surfaces of wafers exposed in such a cleaning process are generally so reactive with other molecules that silicon atoms on the surfaces bond with hydrogen or oxygen, and oxide films are formed. The surfaces of the semiconductor wafers are thus exposed to environmental atmospheres contacting the semiconductor wafers and transiently change.
Semiconductor processes are performed generally in clean rooms, and many systems are used in many steps. When wafers are unloaded from a system to be transferred from a process to another process, the wafers are exposed to the clean room atmosphere. At this time, the wafers are often not only oxidized by oxygen in the air, but also contaminated with certain kinds of contaminants, e.g., organic substances. The wafers are also contaminated with traces of nitrogen oxides, sulfur oxides, etc. It is said that one contamination source of the organic contamination occurring in the clean rooms is organic substances contained in the air in the clean rooms. It is considered that organic substances contained in building materials of the clean rooms, air filters, wires, pipes, etc. are volatilized to produce the organic substances.
Thus, it is very important that quantities of substances contained in the environmental air in a clean room, where a fabrication process of a semiconductor device are conducted, are monitored to identify emission sources of the substances in the environment or control emission amounts of the substances in the environment, thereby increasing fabrication yields and improving performance of semconductor devices.
The environmental monitoring is required not only in the clean rooms for processes for fabricating semiconductor devices, but also in the air of the real environments where we live. Recently it is known that a group of specific substances called xe2x80x9cenvironmental endocrine disrupterxe2x80x9d affects health of humans, and animals and plants. Thus, it is even more necessary to control emission of such substances.
As a conventional method for measuring substances in the atmosphere, e.g., thermal desorption Gas Chromatography/Mass Spectroscopy (GC/MS) is knonw in which substances in the environment are adsorbed by capillary column which is a porous material. The capillary column is heated to release the adsorbed substances, and the released adsorbed substances are identified its species and quantified by mass spectrometric analysis.
However, the above-described conventional measuring method usually takes tens of hours to measure, which makes it difficult to feed back measurement results to the environmental control.
On the other hand, the inventors of the present invention have already proposed an organic contaminant detection method using wafer multiple internal reflection Fourier transform infrared attenuated total reflection spectroscopy (FTIR-ATR) for detecting with high sensitivity organic contaminants staying on the surfaces of wafers (see, e.g., Japanese Patent Application No. Hei 11-95853 (1999). When infrared beam is incident on one end of a wafer at a prescribed incident angle, the infrared beam propagates inside the wafer, repeating total reflections on both surfaces, while the infrared beam penetrates through the wafer surfaces (evanescent wave), and a specific infrared band is absorbed by the organic contaminants staying on the surfaces of the wafer. The propagating light exiting from the other end of the wafer is spectroscopically analyzed by FT-IR to thereby detect and identify the organic contaminants staying on the surfaces of the wafer. In comparison with GC/MS method, this detecting method has the equivalent sensitivity and can perform realtime measurement, as well as simple and economical. Thus, it is considered that application of the multiple internal reflection Fourier transform infrared spectroscopy to the environmental monitoring will make the environmental monitoring highly sensitive and realtime.
An object of the present invention is to provide a method and apparatus for environmental monitoring which can make realtime measurement of high sensitivity by applying multiple internal reflection Fourier transform infrared attenuated total reflection spectroscopy to the environmental monitoring.
The above-described object is achieved by an environmental monitoring method comprising: applying an infrared beam into an infrared transmitting substrate disposed in an environment to be measured; detecting the infrared beam which has undergone multiple internal reflections in the infrared transmitting substrate and exited; spectroscopically analyzing the detected infrared beam to measure a species and/or a quantity of a substance in the environment present near the infrared transmitting substrate; and measuring a species and/or a concentration of the substance in the environment to be measured, based on the species and/or the quantity of the substance in the environment present near the infrared transmitting substrate.
The above-described object is also achieved by an environmental monitoring method comprising: initializing a surface state of an infrared transmitting substrate disposed in an environment to be measured to remove a substance adhered to a surface of the infrared transmitting substrate, in advance of measurement or upon measurement; applying an infrared beam into the infrared transmitting substrate having the surface state initialized; detecting the infrared beam which has undergone multiple internal reflections in the infrared transmitting substrate and exited; spectroscopically analyzing the detected infrared beam to measure a species and/or a quantity of a substance in the environment present near the infrared transmitting substrate; and measuring a species and/or a concentration of the substance in the environment to be measured, based on the species and/or the quantity of the substance in the environment present near the infrared transmitting substrate.
In the above-described environmental monitoring method it is possible that a UV light is irradiated to the infrared transmitting substrate to remove the substance adhering to the infrared transmitting substrate.
In the above-described environmental monitoring method, it is possible that the infrared beam applied into the infrared transmitting substrate is caused to propagate inside the infrared transmitting substrate in one direction, and the infrared beam exited from an end surface other than an end surface on which the infrared beam was incident is detected.
In the above-described environmental monitoring method, it is possible that the infrared beam applied into the infrared transmitting substrate is caused to propagate inside the infrared transmitting substrate in two directions, and the infrared beam exited from the same end surface on which the infrared beam was incident is detected.
In the above-described environmental monitoring method, it is possible that the infrared transmitting substrate includes at least a first propagation path having a longer propagation distance for the infrared beam, and a second propagation path having a shorter propagation distance for the infrared beam; and the first propagation path is used in measuring the substance in the environment with high sensitivity, and the second propagation path is used in measuring the substance in the environment over a wide spectroscopic wavelength range.
The above-described object is also achieved by an environmental monitoring apparatus comprising: an infrared transmitting substrate to which a substance in an environment to be measured is adhered; an infrared source for applying an infrared beam to the infrared transmitting substrate; an infrared spectrometer for detecting and spectroscopically analyzing the infrared beam which has undergone multiple internal reflections in the infrared transmitting substrate and has exited from the infrared transmitting substrate; and a computer for computing a species and/or a quantity of the substance in the environment present near the infrared transmitting substrate, based on a spectroscopic result given by the infrared spectrometer, and computing a species and/or a concentration of the substance in the environment to be measured, based on the species and/or the quantity of the substance in the environment present near the infrared transmitting substrate.
The above-described object is also achieved by an environmental monitoring apparatus comprising: an infrared transmitting substrate to which a substance in an environment to be measured is adhered; an infrared source for applying an infrared beam to the infrared transmitting substrate; an infrared spectrometer for detecting and spectroscopically analyzing the infrared beam which has undergone multiple internal reflections in the infrared transmitting substrate and has exited from the infrared transmitting substrate; a computer for computing a species and/or a quantity of the substance in the environment present near the infrared transmitting substrate, based on a spectroscopic result given by the infrared spectrometer, and computing a species and/or a concentration of the substance in the environment to be measured, based on the species and/or the quantity of the substance in the environment present near the infrared transmitting substrate; and a substance removing means for removing the substance in the environment adhered to the infrared transmitting substrate to initialize a surface state thereof.
In the above-described environmental monitoring apparatus, it is possible that the substance removing means is a UV light irradiating means for irradiating UV light to the infrared transmitting substrate to thereby remove the substance in the environment adhering to the infrared transmitting substrate.
In the above-described environmental monitoring apparatus, it is possible that the UV light applying means comprises a UV source, and a reflecting mirror having an elliptical cross section which is substantially vertical to a propagation direction of the infrared beam; and the infrared source is positioned near one focus of an elliptical face of the reflecting mirror, and the infrared transmitting substrate is positioned near the other focus.
In the above-described environmental monitoring apparatus, it is possible that the infrared transmitting substrate includes at least a first propagation path having a longer propagation distance for the infrared beam, and a second propagation path having a shorter propagation distance for the infrared beam.
In the above-described environmental monitoring apparatus, it is possible that an incidence optical system for applying the infrared beam to the infrared transmitting substrate, and an exit optical system for causing the infrared beam exiting from the infrared transmitting substrate to the infrared spectrometer are disposed on a side of one end surface of the infrared transmitting substrate.
In the above-described environmental monitoring apparatus, it is possible that the infrared transmitting substrate is formed of a material having a transmission band corresponding to a wave number range of not less than 500 cmxe2x88x921 and not more than 5000 cmxe2x88x921.
According to the present invention, concentrations of substances in the environmental atmosphere can be detected with high sensitivity, and their components can be identified. The measurement by the measuring method according to the present invention is realtime, and measured results can be quickly fed back. Accordingly, sources of organic contamination caused in clean rooms can be identified, and quantities of the contamination can be controlled. The environmental monitoring can be made not only in clean rooms, but also in the air of the actual environments where we live. The present invention is useful in controlling emission of the contaminants.